This invention relates to the field of aircraft design, and more particularly to an airplane configuration in which an engine is wholly above a wing, aft deck, or combination thereof and at least in part between vertical stabilizers.
Aircraft engines generate sound and heat in their operation. Excessive sound is undesirable largely because of disturbance to surrounding communities. Heat is undesirable particularly in both military and civil aircraft, which may be tracked by ground-based missiles that seek heat in the form of infrared radiation. The design of the aircraft profoundly impacts the sound and heat that are observed from the ground.
Conventional subsonic civil aircraft designs commonly feature engine placement underneath the airplane's wings. The sound pressure level produced by the engines, herein generally referred to as noise, and particularly engine noise or the “roar” heard at takeoff, travels largely unabated to communities. For under-wing engine installations this noise is amplified by the under-surface of the wing because the portion of the sound produced by the engines that would otherwise radiate upward is reflected downward off of the under-surface. The engine plume interacts with the wing trailing edge. Both the under-surface reflection and the engine plume interaction with the wing trailing edge add to the overall noise heard below. Even when engines are located higher than wings, aircraft generally offer little in the way of impeding the downward travel of sound due to the absence of a surface that covers a substantial extent of the downward sound propagation path. Technological improvements in engines have resulted in a gradual reduction of engine noise over time, but further reductions based on similar improvements will likely be minimal.
Heat similarly radiates from aircraft engines. Some conventional airplane designs having the engines mounted beneath the wings, or the exhaust at the rear end of the aircraft, radiate heat unimpeded to the ground. This issue is exacerbated by the conventional under-wing mount, because radiant heat energy also reflects off the pylon and underside of the wing, much like noise energy.
Transportation and traffic planners frequently call for increasing dependence on regional passenger air transportation to serve substantial areas extending out from major international airport hubs. Aircraft having relatively slow cruise speeds, such as less than about 0.8 mach, and relatively small passenger counts, such as less than about 150 passengers, are often referred to as “regional” aircraft. Regional air transportation poses community environment intrusion as operations are confined within lower speed regimes that result in longer exposure times, at lower altitude ceilings, and over a much larger swath of communities than ever before. Communities in general have become increasingly sensitive to extended exposures to noise and to air safety concerns.
In addition to use as civilian passenger transports, regional jets are used for transport of military commanders and government officials, and are also being evaluated as surveillance platforms. In these military configurations, the regional jet flight regimes and likelihood of operating in increasing hostile threat environments will likely expose the aircraft, at some point, to vehicle-transported and man-portable infrared (IR) air defense systems, which can track and guide on the heat radiated by the aircraft. Asymmetric and non-state threat organizations also exist with access to similar man-portable missiles that could be used to attack civilian aircraft at some time in the future. Defensive systems studies show benefits to reducing or shadowing aircraft signature sources and to giving protective equipment, typically installed on the underside of the aircraft, clear sight lines to the oncoming threat by relocating low hanging engine nacelles and their exhaust plumes.
Another emergent issue associated with increased traffic frequency is the noise produced by thrust-reversing systems. The issue is compounded both by increased traffic and how thrust reversing systems are employed in maximizing operational efficiency. While designed primarily for wet, icy, and slippery runways, airlines often use thrust reversing systems to reduce the time it takes to get to the gate by decelerating quickly to catch early exits and taxiways that are closer to the terminal, as opposed to completing deceleration at the end of the runway and taxiing back to the terminal. Thrust reversing events are typically low frequency in nature, can be heard up to a mile from the airport, and have been demonstrated to cause structure rattle in buildings close to the airport.